The invent relates to a method and apparatus for identifying a gaseous substance and determining its purity, using acoustic techniques. The invention is more particularly concerned with identification of a gaseous substances of unknown species by analysis of frequency response of a resonator containing the substance in vapor form.
In the field of air conditioning service and repair, there is a need to identify the refrigerant charge contained in a system so that the refrigerant can be properly handled for reclamation and recycling, or for disposal. In recent years, because of environmental concerns, it has become the practice for air conditioner repair shops to capture and retain the used refrigerant in a reclamation system, rather than permit it to escape into the atmosphere. Also, because of the high cost of disposal of unreusable refrigerant, and because of the high cost of fresh refrigerant, economic needs have also driven air conditioner repair shops to reclaim the refrigerant charge in a reclaimer device provided for that purpose.
For similar environmental concerns, manufacturers of automotive air conditioning systems have begun to switch over from type R12 refrigerant (dichloro-difluoro methane) to another refrigerant, R134A, (1,1,1,2-tetrafluoroethane) which is believed to be gentler to the environment than R12 if it escapes to the atmosphere. Type R134A refrigerant was engineered to have thermal characteristics very similar to R12 refrigerant so that R134A based systems could be used where R12 systems are now used, i.e., in automotive air conditioning systems. On the other hand, R134A refrigerant is chemically incompatible with R12 refrigerant, and cannot be reused if one refrigerant is contaminated with the other. Also, if either refrigerant R12 or R134A has been contaminated with another refrigerant such as R22, the refrigerant should not be reused. However, if the refrigerant contains air or lubricant, the refrigerant can be deemed acceptable, because the reclaiming device can remove these impurities from the refrigerant.
Techniques of identifying a species of a fluid by means of its dielectric properties have been described e.g. in U.S. Pat. Nos. 5,150,683; 5,091,704; and 5,119,671. For example, the relative percentages of a gasoline/alcohol fuel mixture are measured by applying an RF signal to a coil submerged in the mixture. This system would not be workable for identifying which of two refrigerant species is present and if unacceptable contaminants are present in the refrigerant.
A technique to identify and distinguish between two different refrigerant gases, based on the dielectric properties of the gases, it described in U.S. Pat. No. 5,158,747. The device of that patent can also be configured to be responsive to acoustic properties of the refrigerant vapor, by sensing changes in velocity or phrase angle of acoustic waves traveling in the refrigerant vapor. However, this type of device is not precise enough to sense whether impurities are present in unacceptable levels.